Trane BCHC Two- and Four-Pipe Changeover Operation, Entering Water Temperature Sampling Function

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Table 23. Local fan switch enabled

Communicated	Fan switch (local)	Fan operation fan speed input
Off	Ignored	Off
Low	Ignored	Low
High	Ignored	High
Auto	Off	Off
	Low	Low
	High	High
	Auto	Auto (configured default, determined by heat/cool mode)

Table 24. Fan operation in heating and cooling modes

	Heating		Cooling
Fan mode	Occupied	Unoccupied	Occupied	Unoccupied
Off	Off	Off	Off	Off
Low	Low	Off/high	Low	Off/high
High	High	Off/high	High	Off/high
Auto (continuous)	Default fan speed	Off/high	Default fan speed	Off/high

Two- and Four-Pipe Changeover Operation

Tracer™ ZN controllers offer accurate and reliable unit changeover using 2-way valves and the controller’s entering water temperature sampling function. Only units using the main hydronic coil for both heating and cooling (2-pipe and 4-pipe changeover units) use the entering water temperature sampling function.

Two-pipe and 4-pipe changeover applications require an entering water temperature sensor to allow the main coil to be used for heating and cooling. This sensor is factory-provided and should be field-installed on the entering water pipe.

The entering water temperature sampling function periodically opens the two-way valve to allow temporary water flow, producing reliable entering water temperature measurement. To ensure accurate unit changeover without sacrificing the benefits of 2-way, 2-position valves, Tracer™ ZN controllers periodically test the entering water temperature on all hydronic main coil changeover units. Hydronic heating/cooling changeover operation requires central plant operation, and the unit controller must use an entering water temperature sensor to verify delivery of the correct water temperature from the central plant.

Entering Water Temperature Sampling Function

The entering water temperature (EWT) must be five degrees above the space temperature for hydronic heating and five degrees below the space temperature for hydronic cooling. When water

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